Apache Solr Interview Questions and Answers

Solr (“solar”) is an open source enterprise search platform. It is written in Java from the Apache Lucene project. Its major features include full-text search, hit highlighting, faceted search, real-time indexing, dynamic clustering, database integration, NoSQL features and rich document (Example: Word, PDF) handling. Providing distributed search and index replication, Solr is designed for scalability and fault tolerance. It is widely used for enterprise search and analytics use cases and has an active development community and regular releases.

Solr runs as a standalone full-text search server. It uses the Lucene Java search library at its core for full-text indexing and search and has REST-like HTTP/XML and JSON APIs that make it usable from most popular programming languages. Solr’s external configuration allows it to be tailored to many types of application without Java coding, and it has a plugin architecture to support more advanced customization.

Solr was created by Yonik Seeley in 2004, at CNET Networks as an in-house project to add search capability for the company website.

Apache Solr is an open source search platform built upon a Java library called Lucene. Solr is a popular search platform for Web sites because it can index and search multiple sites and return recommendations for related content based on the search query’s taxonomy. Solr is also a popular search platform for enterprise search because it can be used to index and search documents and email attachments. Solr offers a rich, flexible set of features for search. To understand the extent of this flexibility, it’s helpful to begin with an overview of the steps and components involved in a Solr search.

Request Handler: This, we send to Apache Solr square measure processed by these request handlers. The requests might be question requests or index update requests. based on our requirement, we’d like to pick out the request handler. To pass a request to Solr, we are going to usually map the handler to a precise URI end-point and also the specified request will be served by it.

Search Component: It is a type (feature) of search provided in Apache Solr. It might be spell checking, query, faceting, hit highlighting, etc. These search components are registered as search handlers. Multiple components can be registered to a search handler.

Query Parser: This is parses the queries that we pass to Solr and verifies the queries for syntactical errors. After parsing the queries, it translates them to a format which Lucene understands.

Response Writer: in Apache Solr is the component which generates the formatted output for the user queries. Solr supports response formats such as XML, JSON, CSV, etc. We have different response writers for each type of response.

Analyzer/tokenizer: Lucene recognizes data in the form of tokens. Apache Solr analyzes the content, divides it into tokens, and passes these tokens to Lucene. An analyzer in Apache Solr examines the text of fields and generates a token stream. A tokenizer breaks the token stream prepared by the analyzer into tokens.

Update Request Processor: Whenever we send an update request to Apache Solr, the request is run through a set of plugins (signature, logging, indexing), collectively known as update request processor. This processor is responsible for modifications such as dropping a field, adding a field, etc.

Highlighting Is nothing but the Fragmentation of documents corresponding to the user’s query that is included in the Query response. Afterwards, these fragments are displayed and placed in the special segment that is used by the users and clients to present the snippets. The Solr contains a number of highlighting utilities and has control over various fields. The highlighting utilities can be called by Handlers of Request and can be reused with the standard query parsers.

Apache Solr includes the ability to set up a cluster of Solr servers that combines fault tolerance and high availability is Called SolrCloud, these capabilities provide distributed indexing and search capabilities and the following features:

Central configuration for the entire cluster

Automatic load balancing and fail-over for queries

ZooKeeper integration for cluster coordination and configuration.

In other term SolrCloud is flexible distributed search and indexing, without a master node to allocate nodes, shards and replicas. Instead, Solr uses ZooKeeper to manage these locations, depending on configuration files and schemas. Documents can be sent to any server and ZooKeeper will figure it out:)

When a user runs a search in Solr, the search query is processed by a request handler. SolrRequestHandler is a Solr Plugin, which illustrates the logic to be executed for any request. Solrconfig.xml file comprises several handlers (containing a number of instances of the same Solr Request Handler class having different configurations).

The Tokenizer is used to break a stream of text into a series of Tokens, where each Token is an arrangement of characters in the text. The Token that is developed is then passed to the Token Filters which can update, remove and add the Tokens. Afterwards, that field is indexed by the resulting Token stream.

Also known as Lucence Parser, the Solr standard query parser enables users to specify precise queries through a robust syntax. However, the parser’s syntax is vulnerable to many syntax errors unlike other error-free query parsers like DisMax parser

The Faceting refers to the categorization and arrangement of all search results that depends upon the index terms. The Faceting process makes the searching task more fluent as the users search for the exact results.